Electric drives require for starting (below rated speed), a torque which is a multiple of the rated torque, and for higher speeds (above rated speed), an increased torque. While the first one is required to guarantee a smooth start-up, the latter is desirable to warrant sufficient acceleration torque to improve dynamic performance. It is well known that speed control—based on (V/f) control—results in a decreasing torque above rated operation (Trated, nm—rated).
Rated speed is the maximum speed that an electric motor can run at, while also running at a rated torque, continuously for a significant period of time without damaging the motor. Rated torque is the maximum torque that an electric motor can produce continuously for a significant period of time without damaging the motor.